The present invention relates to a magnetic circuit which can be adjusted easily, and more specifically to an electromagnetically-tuned filter with magnetic poles which can be tilted for adjustment while the filter is operating in test setup.
In a multi-stage electromagnetically-tuned filter, a plurality of ferromagnetic resonators are typically positioned within the same applied magnetic field established between the same set of magnetic pole pieces so that they will ideally resonate at exactly the same frequency. Such resonators are disclosed, for example, in U.S. Pat. No. 3,544,918 issued Dec. 1, 1972 to W. E. Venator, Jr. and U.S. Pat. No. 3,879,677 issued Apr. 22, 1975 to C. A. Arnold. As a practical matter, however, fine adjustments of the magnetic field are necessary because of the existence of edge effects and other types of irregularity, and a most popular method for achieving this tracking has been to place a shim of proper thickness at an appropriate position, for example, between the magnetic circuit structure and the support structure, to tip the pole piece, but this method is not satisfactory because the magnetic circuit structure which typically includes a coil housing which must be removed each time the thickness or position of the shim is changed and the results of adjustments cannot be observed until the filter is reassembled and connected in the test setup. In short, the conventional method of achieving this tracking has been a very difficult time-consuming task.